Refractive eye surgery is optional
eye surgery used to improve the refractive state of the
eye and decrease or eliminate dependency on
glasses
Glasses, also known as eyeglasses or spectacles, are vision eyewear, with lenses (clear or tinted) mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms (known as temples or ...
or
contact lenses
Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmeti ...
. This can include various methods of surgical remodeling of the
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...
(
keratomileusis
Keratomileusis, from Greek κέρας (kéras: horn) and σμίλευσις (smíleusis: carving),The word is derived from Greek κέρας - keras (root: kerat-) "horn, cornea" and σμίλευσις - smileusis "carving or corneal reshaping, is ...
), lens implantation or lens replacement. The most common methods today use
excimer laser
An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
s to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as
myopia,
hyperopia
Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
,
presbyopia
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
and
astigmatism
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
.
History
![MEL60-UOC](https://upload.wikimedia.org/wikipedia/commons/3/3e/MEL60-UOC.jpg)
The first theoretical work on the potential of refractive surgery was published in 1885 by
Hjalmar August Schiøtz, an
ophthalmologist
Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders.
An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Followin ...
from
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
. In 1930, the
Japanese
Japanese may refer to:
* Something from or related to Japan, an island country in East Asia
* Japanese language, spoken mainly in Japan
* Japanese people, the ethnic group that identifies with Japan through ancestry or culture
** Japanese diaspor ...
ophthalmologist
Tsutomu Sato made the first attempts at performing this kind of surgery, hoping to correct the vision of military pilots. His approach was to make radial cuts in the cornea, correcting effects by up to 6
diopters
A dioptre (British spelling) or diopter (American spelling) is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m−1. It is normally used to express the optical power of a lens or cu ...
. The procedure unfortunately produced a high rate of corneal degeneration, however, and was soon rejected by the medical community.
The first proficient refractive surgery technique was developed in the Barraquer ophthalmologic clinic (
Bogotá
Bogotá (, also , , ), officially Bogotá, Distrito Capital, abbreviated Bogotá, D.C., and formerly known as Santa Fe de Bogotá (; ) during the Spanish period and between 1991 and 2000, is the capital city of Colombia, and one of the larges ...
,
Colombia
Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
), in 1963, by
Jose Barraquer
José Ignacio Barraquer Moner (24 January 1916 – 13 February 1998) was a Spanish ophthalmologist and inventor born in Barcelona who did most of his life's work in Bogotá, Colombia.
His original pioneering investigations on corneal transplan ...
. His technique, called
keratomileusis
Keratomileusis, from Greek κέρας (kéras: horn) and σμίλευσις (smíleusis: carving),The word is derived from Greek κέρας - keras (root: kerat-) "horn, cornea" and σμίλευσις - smileusis "carving or corneal reshaping, is ...
, meaning corneal reshaping (from Greek ''κέρας'' (kéras: horn) and ''σμίλευσις'' (smileusis: carving)), enabled the correction, not only of myopia, but also of hyperopia. It involves removing a corneal layer, freezing it so that it could be manually sculpted into the required shape, and finally reimplanting the reshaped layer into the eye. In 1980, Swinger performed first keratomileusis surgery in US.
In 1985, Krumeich and Swinger introduced non-freeze keratomileusis technique,
it remained a relatively imprecise technique.
In 1974 a refractive procedure called
Radial Keratotomy (RK) was developed in the USSR by
Svyatoslav Fyodorov
Svyatoslav Nikolayevich Fyodorov (; August 8, 1927 – June 2, 2000) was a Russian ophthalmologist, politician, professor, full member of the Russian Academy of Sciences and Russian Academy of Medical Sciences. He is considered to be a pioneer o ...
and later introduced to the United States. RK involves making a number of cuts in the cornea to change its shape and correct refractive errors. The incisions are made with a
diamond knife
A diamond knife is a very sharp knife in which the edge is made from diamond, invented by Humberto Fernández-Morán in 1955. Diamond knives are used for medical and scientific applications where an extremely sharp and long-lasting edge is essent ...
. Following the introduction of RK, doctors routinely corrected nearsightedness, farsightedness, and astigmatism using various applications of incisions on the cornea.
Meanwhile, experiments in 1970 using a
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
dimer
Dimer may refer to:
* Dimer (chemistry), a chemical structure formed from two similar sub-units
** Protein dimer, a protein quaternary structure
** d-dimer
* Dimer model, an item in statistical mechanics, based on ''domino tiling''
* Julius Dimer ...
and in 1975 using
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
halides
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
resulted in the invention of a type of
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
called an
excimer laser
An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
. While excimer lasers were initially used for industrial purposes, in 1980,
Rangaswamy Srinivasan, a scientist of
IBM who was using an excimer laser to make microscopic circuits in
microchips
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny M ...
for informatics equipment, discovered that the excimer could also be used to cut organic tissues with high accuracy without significant thermal damage. The discovery of an effective biological cutting laser, along with the development of computers to control it, enabled the development of new refractive surgery techniques.
In 1983, Stephen Trokel, a scientist at
Columbia University
Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhatt ...
, in collaboration with
Theo Seiler
Theo Seiler (born February 12, 1949 in Ravensburg, Germany) is a German ophthalmologist and physicist. He is considered one of the pioneers of refractive surgery.
Biography
Seiler graduated from gymnasium in 1968 and enrolled the same year ...
and Srinivasan, performed the first Photorefractive Keratectomy (PRK), or keratomileusis in situ (without separation of corneal layer) in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. The first patent for this approach, which later became known as
LASIK
LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, sinc ...
surgery, was granted by the US Patent Office to Gholam Ali. Peyman, MD on June 20, 1989. It involves cutting a flap in the cornea and pulling it back to expose the corneal bed, then using an excimer laser to ablate the exposed surface to the desired shape, and then replacing the flap. The name
LASIK
LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, sinc ...
was coined in 1991 by
University of Crete
The University of Crete (UoC; Greek: Πανεπιστήμιο Κρήτης) is a multi-disciplinary, research-oriented institution in Crete, Greece, located in the cities of Rethymno (official seat) and Heraklion, and one of the country's most aca ...
and the Vardinoyannion Eye.
The patents related to so-called broad-beam
LASIK
LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, sinc ...
and PRK technologies were granted to US companies including Visx and Summit during 1990–1995 based on the fundamental US patent issued to IBM (1983) which claimed the use of UV laser for the ablation of organic tissues.
In 1991, J.T. Lin, Ph.D. (a Chinese Physicist) was granted a US patent for a new technology using a flying-spot for customized LASIK currently used worldwide. The first US patent using an eye-tracking device to prevent decentration in LASIK procedures was granted to another Chinese Physicist, Dr. S. Lai in 1993.
Techniques
Flap procedures
Excimer laser ablation is done under a partial-thickness lamellar corneal flap.
*
Automated lamellar keratoplasty
Automated lamellar keratoplasty (ALK), also known as keratomileusis in situ, is a non-laser lamellar refractive procedure used to correct high degree refractive errors.
This procedure can correct large amounts of myopia and hyperopia. However, th ...
(ALK): The surgeon uses an instrument called a
microkeratome
A microkeratome is a precision surgical instrument with an oscillating blade designed for creating the corneal flap in LASIK or ALK surgery. The normal human cornea varies from around 500 to 600 micrometres in thickness; and in the LASIK procedur ...
to cut a thin flap of the corneal tissue. The flap is lifted like a hinged door, targeted tissue is removed from the
corneal stroma
The stroma of the cornea (or substantia propria) is a fibrous, tough, unyielding, perfectly transparent and the thickest layer of the cornea of the eye. It is between Bowman's membrane anteriorly, and Descemet's membrane posteriorly.
At its cent ...
, again with the microkeratome, and then the flap is replaced.
*
Laser-assisted in situ Keratomileusis (LASIK): The surgeon uses either a
microkeratome
A microkeratome is a precision surgical instrument with an oscillating blade designed for creating the corneal flap in LASIK or ALK surgery. The normal human cornea varies from around 500 to 600 micrometres in thickness; and in the LASIK procedur ...
or a
femtosecond laser
Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). A laser operated in this way is sometimes r ...
to cut a flap of the corneal tissue (usually with a thickness of 100–180 micrometres). The flap is lifted like a hinged door, but in contrast to ALK, the targeted tissue is removed from the corneal stroma with an excimer laser. The flap is subsequently replaced. When the flap is created using an IntraLase brand femtosecond laser, the method is called IntraLASIK; other femtosecond lasers such as the Ziemer create a flap similarly. Femtosecond lasers have numerous advantages over mechanical microkeratome based procedure. Microkeratome related flap complications like incomplete flaps, buttonholes or epithelial erosion are eliminated with femtosecond laser procedure.
Absence of microscopic metal fragments from the blade will reduce the risk of lamellar keratitis also.
** Customized aspheric treatment zone (CATz) is a
topography-guided LASIK treatment developed by NIDEK Co. Ltd which ablates the cornea based on patient-specific geometry to address certain disadvantages in conventional wavefront spherocylindrical ablation. The treatment is effective for myopia with
astigmatism
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
or otherwise irregular corneas, and reduces symptoms such as glare, halos, and night driving difficulty.
* Refractive Lenticule Extraction (ReLEx):
** ReLEx "FLEx" (Femtosecond Lenticule Extraction): A femtosecond laser cuts a lenticule within the corneal stroma. Afterwards, a LASIK-like flap is cut which can be lifted to access the lenticule. This is removed through manual dissection using a blunt spatula and forceps.
** ReLEx "SMILE" (
Small Incision Lenticule Extraction): A newer technique without a flap, a femtosecond laser cuts a lenticule within the corneal stroma. The same laser is used to cut a small incision along the periphery of the lenticlue about 1/5th the size of a standard LASIK flap incision. The surgeon then uses a specially designed instrument to separate and remove the lenticule through the incision, leaving the anterior lamellae of the cornea intact. No excimer laser is used in the "ReLEx-procedures".
Surface procedures
The excimer laser is used to ablate the most anterior portion of the corneal stroma. These procedures do not require a partial thickness cut into the stroma. Surface ablation methods differ only in the way the epithelial layer is handled.
*
Photorefractive keratectomy
Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (or laser epithelial keratomileusis) (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lense ...
(PRK) is an outpatient procedure generally performed with local
anesthetic
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...
eye drops (as with LASIK/LASEK). It is a type of refractive surgery which reshapes the cornea by removing microscopic amounts of tissue from the corneal stroma, using a computer-controlled beam of light (
excimer laser
An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
). The difference from LASIK is that the top layer of the epithelium is removed (and a bandage contact lens is used), so no flap is created. Recovery time is longer with PRK than with LASIK, though the outcome (after 3 months) is about the same (very good). More recently, customized ablation has been performed with LASIK, LASEK, and PRK.
*
Transepithelial photorefractive keratectomy (TransPRK) is a laser-assisted eye surgery to correct refraction errors of human eye cornea. It employs excimer laser to ablate outer layer of cornea, epithelium, as well its connective tissue, stroma, to correct eye optical power.
*
Laser Assisted Sub-Epithelium Keratomileusis (LASEK) is a procedure that also changes the shape of the cornea using an
excimer laser
An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
to ablate the tissue from the corneal stroma, under the corneal epithelium, which is kept mostly intact to act as a natural
bandage
A bandage is a piece of material used either to support a medical device such as a dressing or splint, or on its own to provide support to or to restrict the movement of a part of the body. When used with a dressing, the dressing is applie ...
. The surgeon uses an alcohol solution to loosen then lift a thin layer of the epithelium with a trephine blade (usually with a thickness of 50 micrometres). During the weeks following LASEK, the epithelium heals, leaving no permanent flap in the cornea. This healing process can involve discomfort comparable to that with PRK.
*
EPI-LASIK Epi-LASIK is a refractive surgery technique designed to reduce a person's dependency on eyeglasses and contact lenses. Invented by Dr. Ioannis Pallikaris, the technique is basically an automatic LASEK without alcohol; it can be better considered as ...
is a new technique similar to LASEK that uses an epi-keratome (rather than a trephine blade and alcohol), to remove the top layer of the epithelium (usually with thickness of 50 micrometres), which is subsequently replaced. For some people it can provide better results than regular LASEK in that it avoids the possibility of negative effects from the alcohol, and recovery may involve less discomfort.
*
Customized Transepithelial No-touch (C-TEN) is an innovative strategy for corneal surgery that avoids any corneal manipulation via a complete laser-assisted trans-epithelial approach. Since C-TEN is planned on the morphology of each individual eye, it can treat a large variety of corneal pathologies from refractive to therapeutic. C-TEN is sometimes referred to as Advanced Surface Ablation (ASA)
Corneal incision procedures
*
Radial keratotomy (RK), developed by Russian ophthalmologist
Svyatoslav Fyodorov
Svyatoslav Nikolayevich Fyodorov (; August 8, 1927 – June 2, 2000) was a Russian ophthalmologist, politician, professor, full member of the Russian Academy of Sciences and Russian Academy of Medical Sciences. He is considered to be a pioneer o ...
in 1974, uses spoke-shaped incisions, always made with a diamond knife, to alter the shape of the cornea and reduce
myopia or
astigmatism
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
; this technique is, in medium to high diopters, usually replaced by other refractive methods.
* Arcuate keratotomy (AK), also known as Astigmatic keratotomy, uses curvilinear incisions at the periphery of the cornea to correct high levels of non-pathological astigmatism, up to 13 diopters. AK is often used for the correction of high post-keratoplasty astigmatism or post-cataract surgery astigmatism.
*
Limbal relaxing incisions
Limbal relaxing incisions (LRI) are a refractive surgical procedure to correct minor astigmatism in the eye. Incisions are made at the opposite edges of the cornea, following the curve of the iris, causing a slight flattening in that direction. B ...
(LRI) are incisions near the outer edge of the iris, used to correct minor astigmatism (typically less than 2 diopters). This is often performed in conjunction with an Intraocular Lens implantation.
Other procedures
*
Radial Keratocoagulation, also known as ''Radial Thermokeratoplasty'', was invented in 1985 by
Svyatoslav Fyodorov
Svyatoslav Nikolayevich Fyodorov (; August 8, 1927 – June 2, 2000) was a Russian ophthalmologist, politician, professor, full member of the Russian Academy of Sciences and Russian Academy of Medical Sciences. He is considered to be a pioneer o ...
and is used to correct
hyperopia
Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
by putting a ring of 8 or 16 small burns surrounding the pupil, and steepen the cornea with a ring of collagen constriction. It can also be used to treat selected types of astigmatism. It is now generally replaced by laser thermal keratoplasty/laser thermokeratoplasty.
*
Laser thermal keratoplasty
Laser thermal keratoplasty is a non-contact laser refractive surgery.
__TOC__ Procedure
The procedure employs a holmium laser to place a ring of concentric laser burns on the cornea between 6 mm and 7 mm in diameter. These burns cause a ...
(LTK) is a non-touch thermal keratoplasty performed with a
Holmium
Holmium is a chemical element with the symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like a lot of othe ...
laser, while
conductive keratoplasty
Conductive keratoplasty (CK) is a type of refractive surgery that uses radio waves to adjust the contour of the cornea by shrinking the corneal collagen around it. It is used to treat mild to moderate hyperopia. It is a non-invasive alternative ...
(CK) is thermal keratoplasty performed with a high-frequency electric probe. Thermal keratoplasty can also be used to improve presbyopia or reading vision after age 40.
*
Intrastromal corneal ring segments (Intacs) are approved by FDA for treatment of low degrees of myopia.
*
Phakic intraocular lens
A phakic intraocular lens (PIOL) is a special kind of intraocular lens that is implanted surgically into the eye to correct myopia (nearsightedness). It is called "phakic" (meaning "having a lens") because the eye's natural lens is left untouched. ...
(
PIOL) implantation inside the eye can also be used to change refractive errors. The newest type of intervention is a type of PIOL called the
implantable collamer lens
Intraocular lens (IOL) is a lens implanted in the eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic, or false lens. Such a lens is typically i ...
(
ICL) which uses a biocompatible flexible lens which can be inserted in the eye via a 3 mm incision. The ICL is used to correct myopia ranging from −0.5 to −18 diopters, and +0.5 cylinder power to +6.0 for the Toric ICL models.
* Generally refractive surgery can be broadly divided into: corneal surgery, scleral surgery, lens related surgery (including phakic IOL implantation, clear lens extraction, photophacoreduction and photophacomodulation for correction of presbyopia)
* For presbyopia correction, a
corneal inlay A corneal inlay (also called an intracorneal implant) is a device which is surgically implanted in the cornea of the eye as a treatment for presbyopia. Successful installation results in reducing dependence on reading glasses, so that the user can ...
consisting of a porous black ring surrounding a small clear aperture was originally developed by D. Miller, H. Grey PhD and a group at Acufocus. The inlay is placed under a LASIK flap or in a stromal pocket.
Using mid-IR and UV lasers for the treatment of presbyopia by scleral tissue ablation was first proposed and patented by J.T. Lin, Ph.D. in US patents #6,258,082 (in 2001) and #6,824,540 (in 2004).
Expectations
Research conducted by the Magill Research Center for Vision Correction, Medical University of South Carolina, showed that the overall patient satisfaction rate after primary LASIK surgery was 95.4%. They further differentiated between myopic LASIK (95.3%) and hyperopic LASIK (96.3%). They concluded that the vast majority (95.4%) of patients were satisfied with their outcome after LASIK surgery.
Ophthalmologists use various approaches to analyze the results of refractive surgery, and alter their techniques to provide better results in the future.
Some of these approaches are programmed into the devices ophthalmologists use to measure the refraction of the eye and the shape of the cornea, such as
corneal topography
Corneal topography, also known as photokeratoscopy or videokeratography, is a non-invasive medical imaging technique for mapping the anterior curvature of the cornea, the outer structure of the eye. Since the cornea is normally responsible for s ...
.
Risks
While refractive surgery is becoming more affordable and safe, it may not be recommended for everybody. People with certain
eye disease
This is a partial list of human eye diseases and disorders.
The World Health Organization publishes a classification of known diseases and injuries, the International Statistical Classification of Diseases and Related Health Problems, or ICD-10. ...
s involving the
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...
or
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
, pregnant women, and patients who have medical conditions such as
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
,
diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...
, uncontrolled vascular disease, or autoimmune disease are not good candidates for refractive surgery.
Keratoconus, a progressive thinning of the cornea, is a common corneal disorder. Keratoconus occurring after refractive surgery is called
Corneal Ectasia. It is believed that additional thinning of the cornea via refractive surgery may contribute to advancement of the disease that may lead to the need for a
corneal transplant
Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue (the graft). When the entire cornea is replaced it is known as penetrating keratoplasty ...
. Therefore, keratoconus is a
contraindication
In medicine, a contraindication is a condition that serves as a reason not to take a certain medical treatment due to the harm that it would cause the patient. Contraindication is the opposite of indication, which is a reason to use a certain tre ...
to refractive surgery. Corneal topography and
pachymetry
Corneal pachymetry is the process of measuring the thickness of the cornea. A pachymeter is a medical device used to measure the thickness of the eye's cornea. It is used to perform corneal pachymetry prior to refractive surgery, for Keratoconu ...
are used to screen for abnormal corneas. Furthermore, some people's eye shape may not permit effective refractive surgery without removing excessive amounts of corneal tissue. Those considering laser eye surgery should have a full
eye examination
An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ...
.
Although the risk of complications is decreasing compared to the early days of refractive surgery, there is still a small chance for serious problems. These include vision problems such as ghosting, halos, starbursts, double-vision, and dry-eye syndrome. With procedures that create a permanent flap in the cornea (such as LASIK), there is also the possibility of accidental traumatic flap displacement years after the surgery, with potentially disastrous results if not given prompt medical attention.
For patients with
strabismus
Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a ...
, risks of complications such as
diplopia
Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often v ...
and/or increased strabismus angle need to be evaluated carefully. In case both refractive surgery and
strabismus surgery are to be performed, it is recommended that the refractive surgery be done first.
Children
Pediatric refractive surgery involves other risks than refractive surgery on adults, yet it may be indicated especially for children whose cognitive or visual development is failing due to refractive error,
[Erin D. Stahl: ''Pediatric refractive surgery'']
p. 41
In: in particular in cases of bilateral high refractive error,
anisometropia
Anisometropia refers to a condition when two eyes have unequal refractive power. Generally, a difference in power of one diopter (1D) or more is the accepted threshold to label the condition anisometropia. Patients can tolerate 3 D of anisomet ...
,
anisometric
amblyopia
Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
[Erin D. Stahl: ''Pediatric refractive surgery'']
p. 44–46
In: [Kenneth W. Wright, Mehmet Cem Mocan, ''My experience with pediatric refractive surgery''. In: ] or
accommodative esotropia
Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usual ...
.
Interventions on young children may require general anaesthesia in order to avoid risks due to involuntary movement, and children have a higher risk of rubbing or manipulating their eyes post-surgically. Changes to refractive error occurring during normal age development need to be accounted for, and children have a higher risk of developing postoperative corneal haze.
[Erin D. Stahl: ''Pediatric refractive surgery'']
p. 46–47
In: This risk is particularly relevant with relation to
myopic
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...
children.
One study evaluated the outcome of LASEK interventions on 53 children aged 10 months to 16 years who had
anisometropic amblyopia
Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
. The choice of LASEK was made as it was felt it would give fewer complications than LASIK and less post-operative pain than PRK. In the intervention, which was performed under general anaesthesia, the refractive error in the weaker eye was corrected to balance the refractive error of the other eye.
Strabismus surgery was performed later if required. After one year, over 60% had improved in best corrected visual acuity (BCVA) in the weaker eye. Notably, over 80% showed
stereopsis
Stereopsis () is the component of depth perception retrieved through binocular vision.
Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image becaus ...
post-operatively whereas less than 40% had showed stereopsis before.
In addition to corneal refractive procedures (LASIK, PRK and LASEK), intraocular refractive procedures (
phakic intraocular lens
A phakic intraocular lens (PIOL) is a special kind of intraocular lens that is implanted surgically into the eye to correct myopia (nearsightedness). It is called "phakic" (meaning "having a lens") because the eye's natural lens is left untouched. ...
es,
refractive lens exchange and clear lens extraction) are also performed on children.
[Evelyn A. Paysse: ''Refractive surgery in children'', ]
See also
*
Orthokeratology
Orthokeratology, also referred to as Night lenses, Ortho-K, OK, Overnight Vision Correction, Corneal Refractive Therapy (CRT), Accelerated Orthokeretology, Cornea Corrective Contacts, Eccentricity Zero Molding, and Gentle Vision Shaping System (GVS ...
– contact lenses worn only at night to reshape the eye.
References
External links
DJO, Digital Journal of Ophthalmology
{{DEFAULTSORT:Refractive Surgery
Eye surgery
Refraction